Upper GI tract Flashcards
What is digestion?
Process of breaking down macromolecules to allow absorption
What is absorption?
The process of moving nutrients and water across a membrane
What are the components of the GI system?
Salivary glands Oesophagus Sublingual glands Submandibular glands Stomach Duodenum Colon
What are the foregut structures?
Liver Pancreas Oesophagus Stomach Billary system
What are the midgut structures?
Small intestine
Part of large
What are the hind gut structures?
Colon
Rectum
What are the layers of the gut wall?
Mucosa (epithelium)
Submucosa
Musularis
Serosa/Adeventitia
What is the function of the mucosa?
Secretory and absorptive functions
What is the function of the submucosa?
Contains blood vessels and capillaries that facilitate exchange
What is the function of the muscularis?
Facilitates peristalis
Inner layer- circular muscle that constricts the bowel and divides bowel into segments so that food stays in segments for some time to prevent food rushing through
Longitudinal layer- propagates food through GI tract
What is the function of the serosa?
Connective tissue
Describe the numbers of teeth
8 incisors
4 canines
8 premolars
12 molars
What are the muscles in the oral cavity?
Masseter- largest jaw muscle
responsible for biting
Several others that control the position of mandible
What do the salivary glands do?
Secrete lipase and amylase
What do the tongue muscles do?
Propagate the food into the pharynx
What does the pharynx lead to?
Oesophagus
What do the intrinsic muscles of the tongue do?
fine motor control & moving food
What do the extrinsic muscles of the tongue do?
gross movement of tongue (in, out, up & down)
Assists mechanical digestion
What is the function of the oesophagus?
Conduit for food, drink & swallowed secretions from pharynx to stomach
What is the structure and function relationship of the oesophageal epithelium?
Non-keratinising
‘Wear & Tear’ lining (extremes of temp. & texture)
Lubrication – Mucus secreting glands (& saliva)
What muscles are in the oesophagus?
Upper and lower oesophageal sphincter
Play a role in how food gradually moves into the oesophagus
Function not fully understood
What is the structure and function relationship of the oesophageal muscles?
Tonically active
Swallowing centre
What is gastro-oesophageal reflex disease?
Acid refluxes into the oesophagus
‘Heart-burn’
Burning sensation
What results from acid reflux?
Inflammation of the oesophagus Red streaks- oesophagitis After many years lining changes from squamous to columnar epithelium to protect oesophagus against acid "Metaplasia"- Barret's oesophagus Pre-malignant condition
What should be done in a patient with barret’s?
Surveillance endoscopsy every 2-3 years
To detect dysplasia
What is the function of the inner circular muscle?
Divided oesophagus into segments
Pushes food through
What is the function of the longitudial muscles?
Facilitates peristalsis
What are the main features of the gastro-oesophageal junction?
Reflux – prevented by diaphragm
Epithelial transition
Gastric folds - rugae
What is the diaphragmatic hiatus?
The diaphragm pinches the lower end of the oesophagus
Helps prevent acid reflux
How else is acid reflux prevented on a regular basis?
Angle between oesophagus and stomach is acute
2cm of oesophagus in abdo
Negative pressure in thorax
Positive pressure in abdo
The differential keeps the 2cm in abdo in collapsed state
What is a hiatus hernia?
Hiatus becomes large
Stomach migrates into chest Keeps gastro-oesophageal junction open
Causes acid reflux
What is a giant hiatus hernia?
Entire stomach migrates to chest
Collapsed lungs
Reduced lung capacity
Breathlessness
Why are gastric folds present?
Absorbing function
Folds contains villi to increase the SA
Allows for the absorption of plentiful nutrients
What are the 4 phases of swallowing?
0: Oral Phase
1: Pharyngeal phase
2: Upper oesophageal phase
3: Lower oesophageal phase
What happens during oral the phase?
Chewing & saliva prepare bolus
Both oesophageal sphincters constricted
What happens during the pharyngeal phase?
Pharyngeal musculature guides food bolus towards oesophagus
Both oesophageal sphincters open
What happens during the upper oesophageal phase?
Upper sphincter closes
Superior circular muscle rings contract & inferior rings dilate
Sequential contractions of longitudinal muscle
What happens during the lower oesophageal phase?
Lower sphincter closes as food passes through
What are the functions of the stomach?
Breaks food into smaller particles (acid & pepsin)
Holds food, releasing it in controlled steady rate into duodenum
Kills parasites & certain bacteria
What are the different parts of the stomach?
Cardia and pyloric region
Body and fundus
Antrum
How much acid is secreted by the stomach a day?
2L/day
What is the function of stomach acid?
Breaks down food and starts process of digestion
What is segmentation?
Keeps food in stomach 80% stomach contractions Weaker. Fluid chyme towards Pyloric sphincter Solid chyme pushed back to body Stretching activates enteric NS
What is peristalsis?
20% stomach contractions
Propels chyme towards colon
more powerful as moves from LOS to pyloric sphincter
ANS essential
What are the main cells present in the stomach?
Chief cells
Parietal cells
What are the main features of the gastric chief cells?
Protein-secreting epithelial cell
Abundant RER- involved in synthetic production of proteins
Golgi packaging and modifying for export
Masses of apical secretion granules
Secretes pepsinogen to be converted to pepsin
What are the main features of the parietal cells?
Active pump
Many mitochondria (requires lots of ATP)
Cytoplasmic tubulovesicles (contain H+/K+ ATPase)
Internal canaliculi (extend to apical surface)
Tubulovesicles fuse with membrane
Microvilli project into canaliculi
Release HCL into lumen
How is HCL produced?
clarify
CO2 come from capillaries into parietal cells
Mixes with H2O catalysed by carbonic anhydrase
Potassium enters cell
Gets secreted into gastric lumen
Balance maintained by Na+ entering capillaries
Potassium exchanged with H+ ion through H+/K+ ATPase pump
Bicarbonic acid goes back into circulation
H+ combines with CL-
What is the main function of HCL?
converts pepsinogen to pepsin
What is gastrin?
Hormone secreted by G-cells in pyloric antrum
Stimulates HCL secretion from parietal cell
Stimulates histamine release from chromaffin cells
What is a gastrinoma?
Benign tumour of gastrin producing cells
Often in pancreas
Presents with persistent and multiple ulcers
What stimulates parietal cells?
Neurostimulation: Thought, sight, smell & taste of food via vagus nerves
Hormonal stimulation: pancreas secreting gastrin acts on parietal cells
Local stimulation: local reflexes via neural plexus’
What is the function of enterohormones?
Play in a role in the enter-gastric reflex
Suppresses or enhances production of HCL and gastrin
